The condensation products of formaldehyde with ureas are well known substances widely employed to prepare thermoset resins which find a multitude of uses as adhesives, coatings, binders, and as finishes for paper, wood and textiles.
Urea-formaldehyde resins are in themselves rather incombustible. However, when they are applied to combustible substrates such as paper, cloth, wood, or the like, the resulting combination is often highly combustible. It has been known that the addition of such phosphorus containing additives as phosphoric acid, ammonium phosphate and the like markedly reduces the flammability of the products resulting from the combination of urea-formaldehyde resins with combustible substrates. However, such additives are readily removed upon even a minimal leaching with water. Thus, for uses where resistance to water is necessary as in coatings, apparel fabrics, paper, wood, plywood, and the like, these additives do not provide sufficiently durable, flame-retarding compositions.
The literature describes previous attempts to prepare urea derivatives having organic phosphorus groups attached to the nitrogen atoms of the urea, e.g. U.S. Pat. No. 3,393,253. However, the resulting compounds have direct Phosphorus-to-nitrogen bonds which results in their having less than the desired degree of hydrolytic stability. Moreover, such compounds must be made through the use of the dangerously unstable N-chlorourea intermediate.
It is, therefore, the prime object of this invention to provide stable, urea derivatives having organically bound phosphorus substituted thereon. It is a further object to provide phosphorus substituted urea derivatives useful for conducting condensation or co-condensation reactions which yield aminoplastic resins having utility as durable flame retardant coatings, binders, adhesives, and finishes for various substrates including textiles and paper as well as for use as molding resins. It is still another object to make available new processes for preparing these phosphorus containing urea derivatives. Various other objects and advantages of this invention will be apparent from a reading of the disclosure which follows hereinafter.